PAOs comprise a class of hydrocarbon lubricants which has achieved importance in the lubricating oil market. These materials are typically produced by the catalytic oligomerization (polymerization to low-molecular-weight products) of α-olefins typically ranging from 1-octene to 1-dodecene, with 1-decene being a preferred material, although polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins, as described in U.S. Pat. No. 4,956,122 and the patents referred to therein. PAO products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2 cSt at 100° C. to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100° C.
The PAO's are typically produced by the polymerization of olefin feed in the presence of a catalyst such as AlCl3 or BF3. Processes for the production of PAO lubricants are disclosed in numerous patents, for example, U.S. Pat. Nos. 3,149,178; 3,382,291; 3,742,082; 3,780,128; 4,172,855 and 4,956,122.
High viscosity PAOs (defined herein as PAOs having a kinematic viscosity at 100° C. of >20 cSt as measured by ASTM D 445) are normally produced via cationic oligomerization of linear alpha olefins. 1-decene is the preferred olefin for oligomerization. PAOs have also been produced using mixtures of olefins containing 1-octene and 1-dodecene as well as 1-decene and 1-dodecene.
High viscosity PAOs produced via AlCl3 catalyzed olefin oligomerization have been available commercially for many years, e.g., from ExxonMobil Chemical Company. These PAOs are produced either from 1-decene, or from mixtures containing 1-octene, 1-decene and/or 1-dodecene. When oligomerizing olefin mixtures, the composition needs to be carefully controlled to produce PAOs with the desired blend of low temperature properties including pour point, viscosity, and appearance. Typically, use of olefins with molecular weight greater than 1-decene results in PAOs with high pour points. As a result, when oligomerizing olefin mixtures, a combination of low and high molecular weight olefins (with respect to 1-decene) is generally used.
U.S. Pat. No. 4,533,782 is directed to polymerizing cationically polymerizable monomers including C3-C14 linear or branched 1-olefins using a catalyst comprising an aluminum compound of the formula RnAlX3-n and a compound having the formula R′X (X being a halide in both formulas) in solution.
U.S. Pat. No. 5,196,635 discloses the use of a catalyst prepared by reacting in an organic solvent an aluminum halide and a proton donor useful in oligomerizing C6 to C20 straight chain alpha olefins.
U.S. Pat. No. 6,646,174 teaches a process for oliogmerization of 1-dodecene and 1-decene to produce a PAO product having a kinematic viscosity in the range of from about 4 to about 6 cSt at 100° C. and a viscosity index of 130 to 145, and a pour point of −60° C. to −50° C.
U.S. Pat. No. 6,686,511 directed to a process for making a lube base stock having at least four steps, including separation of an olefinic feedstock in a first separator into fractions and contacting a light olefin fraction with a first oligomerization catalyst in a first oligomerization zone to produce a first product, which is subsequently contacted with a medium olefin fraction and an oligomerization catalyst in a second oligomerization zone to produce a second product.
U.S. Pat. No. 6,395,948 discloses the use of an acidic ionic liquid oligomerization catalyst, described by the general formula Q+A−, for the preparation of high viscosity PAOs from decene or dodecene in the absence of an organic diluent. See also U.S. Application Nos. 2002/0128532 and 2004/0030075.
JP1095108 is directed to a method for manufacturing an olefin oligomer using a Lewis acid and an alkyl cyclohexane.
RU2212936 is directed to a cationic oligomerization of olefins that uses a catalyst containing active aluminum and a co-catalyst that is an organohalide compound RX, where R is a primary, secondary, or tertiary alkyl, allyl, benzyl, acetyl or benzoyl and X is chlorine, bromine or iodine.
Additional patents of interest include WO 99/38938 and U.S. Pat. Nos. 6,706,828 and 6,713,582.
Current practice does not provide enough flexibility in the choice of feed olefin/olefin mixtures that can lead to an economic method of achieving a high viscosity PAO composition having adequate low temperature performance suitable for end use applications such as industrial lubricants.
The present inventors have surprisingly discovered a method of producing high viscosity PAOs having excellent low temperature performance from a mixture containing hexene/dodecene/tetradecene (C6/C12/C14) linear alpha olefins.